Propulsion simulation on fully appended ship model

This study presents the numerical investigation for the flow around the propeller of the ONR Tumblehome combatant in open water and for the flow around the same ship in the case of self-propulsion with actuator disk method. Computational Fluid Dynamics based on RANS-VOF solver have been used in order to analyse the flow. The free surface treatment is multi-phase flow approach, incompressible and nonmiscible flow phases are modelled through the use of conservation equations for each volume fraction of phase. Accuracy involves close attention to the physical modelling, particularly the effects of turbulence, as well as the numerical discretization.

Second Generation Intact Stability Criteria Fallout on Naval Ships Limiting KG Curves

The International Maritime Organization (IMO) finalized the Second Generation Intact Stability Criteria (SGISC), in February 2020. They are intended to be included in Part A of the 2008 International Code on Intact Stability in the following years. The SGISC consider five modes of dynamic stability failure in waves: parametric roll, pure loss of stability, surf-riding/broaching to, dead ship condition and excessive acceleration. In this paper, two semi-displacement, round bilge and transom stern hull forms, the parent hull of the Systematic Series D and the ONR Tumblehome, i.e. typical naval hull forms, are examined. Although naval ships are not directly impacted by SGISC, they are sensitive to dynamic stability failure phenomena due to their geometry and range of service speeds. The procedures to assess the ship vulnerability to the dead ship condition and excessive acceleration criteria, referring to the latest drafts of the criteria (SDC 7/5, 2019), were implemented in Matlab®,. The limiting KG curves associated with this set of criteria were obtained for each vessel. The minimum allowable KG curve associated with the excessive acceleration criterion was compared with the maximum allowable KG curve associated with dead ship condition, to investigate the existence of a safe operational area.

URANS Simulation of ONR Tumblehome Parametric Rolling in Regular Head Waves

In this paper, an in-house CFD code HUST-Ship is used for the numerical simulation of parametric rolling phenomena of ONR Tumblehome in regular head wave. Preliminary resistance and roll decay simulations at Fr = 0.2 were carried out and compared with existed INSEAN experimental data. Following, three DOFs’ ship motions in regular head wave with an initial roll angle of 30 degrees was calculated to examine the possibility of occurrence of parametric rolling. Finally, a simulation without initial roll disturbance was performed to investigate its influence to the steady roll amplitude. By conducting fast Fourier transform of the time history of motions, forces and moments, the characteristics are analyzed and co-related with wave frequency. Results can be concluded that the in-house code has the ability to perform the parametric rolling simulation, and that the final steady roll amplitude is not affected by the initial disturbance. In addition, heave and pitch motions are dominantly affected by wave characteristic, roll frequency is about half that of wave, and that forces and moments in x direction exhibit high-order non-linearity.

Direct Simulations of Turning Circle Maneuver in Waves Using RANS-Overset Method

In the present work, a RANS-overset method is used to numerically investigate turning circle maneuver in waves for a twin-screw ship. CFD solver naoe-FOAM-SJTU is used for the numerical computations of the fully appended ONR Tumblehome ship model. Overset grids are used to fully discretize the ship hull, twin propellers and rudders. The simulation of turning circle maneuver is carried out at constant propeller rotational speed with 35° rudder deflection. Open source toolbox waves2Foam is utilized to generate desired waves for the moving computational domain. Predicted ship trajectory and 6DoF motions, hydrodynamic forces and moments acting on the ship and the moving components are presented. The main parameters of the turning circle maneuver, such as the advance, the transfer, the tactical diameter, and the turning diameter, are presented and compared with the available experiment. Wave effects on the free running turning circle maneuver are discussed through detailed flow visualizations. The trajectory and main parameters agree well with the experiment, which show that the present RANS-overset method is a reliable approach to directly simulate turning circle maneuver in waves.